A rotary mower can comprise a mounting bar laterally mountable on a tractor, one or more pairs of counter-rotating mowing drums rotatably mounted on the underside of the bar with their axes of rotation substantially upright, and at least one cutting blade mounted on the bottom of each of the mowing drums, the cutting diameters for cutting tools mounted on adjacent mowing drums overlapping each other to provide complete cutting over their entire cutting width; the mowing drums are rotatably driven by a power take-off from the tractor.
In U.S. Pat. No. 4,269,019 issued Mar. 29, 1981 to Gerhard Strobel and U.S. Pat. No. 4,030,275 issued June 21, 1977 to Hermann Ruprecht the structure of the mowing drums and their cutting tools is described in detail. These mowing drums generally comprise a cylindrical portion attached to a lower outwardly flared skirt having usually a plurality of cutting blades, and a central shaft mounted on the support. U.S. Pat. No. 4,030,275 describes a flap or deflection plate attached adjacent the mowing drum to help form a proper swath, and an improved flared skirt, which helps prevent clogging, while the swath is being formed. U.S. Pat. No. 3,965,658 describes mowing drums having an upper conical surface having air holes and lower openings through which air can pass during rotation, so that air is properly directed during cutting and does not interfere with swath formation.
Mowers can have two adjacent mowing drums rotating in opposite directions, as taught in U.S. Pat. Nos. 3,965,658, 4,192,123, and German Patent Document open application No. DE-OS 27 03 043.
The harvested cuttings are deposited between the adjacent counter-rotating mowing drums, in a windrow behind the mowing attachment and usually in the center of the cutting swath.
A disadvantage of a rotary mower with a pair or pairs of counter-rotating mowing drums is that with the standard tractor the track widths of the tractor are such that during cutting a previously formed swath deposited by the rotary mowing attachment can be run over by the wheels of the tractor during the cutting of the next swath.
In order to eliminate this disadvantage, it is known, as taught in German Patent Document No. DE-OS 27 03 043, to make the cutting diameter for the cutting tool on the mowing drum positioned furthest from the tractor larger than the cutting diameter for the cutting tool on the mowing drum positioned closest to the tractor in a rotary mowing attachment with two rotating mowing drums, so that the mowing width is increased to such an extent that the conventional tractor with commonly employed track spacing will no longer run over its previously deposited swath. In this known rotary attachment a widening of the crop windrow also occurs, that is there is an increase in the windrow width which corresponds to half the difference between the diameters of the mowing drums, and is small by comparison to the total cutting width or swath width of the rotary mowing attachment.
There is a limit to the size to which two rotors or mowing drums can be increased to increase the cutting swath width of the rotary mowing attachment. When the mowing drums are too large the single windrow formed may be too large and may clog the cutter and prevent conditioning in a convenient manner. Mowing drums which are too large may be inconvenient to mount in the cutter or may be difficult to properly design. Naturally, it is therefore desirable to provide a rotary mowing attachment, having an increased mowing width or cutting swath, but with a minimum windrow or deposited-material width.